Disclaimer:
In order to root your Android device, we will require to flash a rooting kernel to your phone. We will be flashing a rooting kernel in your Galaxy S3 I9300 running on XXUFMB3 Android 4.2.1 Jelly Bean official firmware using ODIN. This will root your device. However, in this process you may lose your personal data and settings.

Please do also note that once your device is rooted, you warranty will be considered void by the OEM. You can, however, reclaim the warranty by re-applying official firmware update.

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Guide to Root XXUFMB3 Android 4.2.1 Jelly Bean on Galaxy S3 I9300

Extract Odin zip file to get Odin3 v3.07.exe.

Switch your phone off. And make sure that you wait 5-6 seconds to confirm complete the power down cycle.

You will then put your Galaxy S3 I9300 phone in Download Mode by pressing and holding down the Volume Down button, alongside Home and the Power button. A screen will then come up; warning you about entering into Download Mode, press the Volume Down key to continue to enter Download Mode.

Run Odin3 v3.07.exe with Administrator rights.

Now that you are all prepared to root your phone, connect your Galaxy S3 I9300 with your PC. You will then see a notification appear in Odin in the bottom left saying “Added!!”. If for some reason, you do not see the said notification, try another USB port. If that too doesn’t work, then reinstall the USB driver. Once you successfully see the “Added!!” notification in Odin, you are good to go. Also, check for COM port being depicted by a number in ‘yellow’ to make sure that you have successfully added your device.

Select these files in Odin at their respective buttons:

Click the PDA Button, and select the CF-Root-SGS3-v6.4.zip file.

In Odin window, make sure Auto Reboot and F. Reset Time checkboxes are selected.

Hit the START button to begin the flashing process.

Once the flashing process is completed, the phone will automatically reboot and you will see a ‘Green’ PASS notification in the top-left-most box. You can unplug the device from the computer now.

Your Galaxy S3 I9300 running XXUFMB3 Android 4.2.1 Jelly Bean firmware is now rooted. If there are any issues, feel free to post in the comments section for our staff to take a look at it.